On 2011-03-19, at 12:37 PM, Michal Seta wrote:
Thank you all for your comments, this discussion makes it all much clearer for me, especially the role of the LED indicator. I too believe that the intuitive/social aspect is more appropriate for PLSS. In any case, I had no intention of interfering with the original goals and philosophy of PLSS but I think I needed a better understanding. I was under a wrong impression, for instance, that the LED was to serve as a binary indicator.
See my other inline comments below:
(> blue Morgan, >> red Xin Wei)
> The ONLY qualities that we should try to guarantee is that, for each given sensor in each given location:
> I think that in addition to these two qualities, we should also do our best to insure that reading the LED's is an unambiguous as possible. This is the argument for using digital – going the analog route, given that we do not have a tremendous amount of expertise or time available, will result in an effectively linear relationship between the output of the sensor (which varies linearly with measured soil humidity) and the brightness of the LED, which leads to a very ambiguous signal.
> I don't think that a reading of only one LED can be unambiguous (unless it is simply a matter of on/off situation which I don't believe is the preferred solution here). My reading of Xin Wei's comments is that letting the human interpret the LED is part of the equation.
>> This should be MUCH easier to implement, MUCH less work.
> I actually disagree here. I think that passing the sensor values through the microcontroller and back out to the LED's will be slightly more work than making a delicate analog circuit, attaching it to each sensor, and water-proofing it, especially since I think we would need to use an op-amp + a few resistors per sensor. I have aesthetic preference for simple analog solutions vs. verbose digital solutions however.
Am I reading this correctly? You mean building n copies of analog circuit and water-proofing them is less work than incorporating one more wire into the design and writing one program (with n instantiations of 1 class)? In any case, I am definitely in favor of an elegant analog solution. Do we actually need an op-amp and a few resistors? I understand that there is some concern about linear vs. non-linear solution but in the long run, if left to humans, they will learn to interpret the reading regardless of it being linear or not. I think that a simple solution (LED + resistor) will yield a reliable reading of the soil's humidity.
>> Use analog first. Digital only when you must, and understand what reductions you are incurring.